IP Addresses Classful Addressing CONTENTS INTRODUCTION CLASSFUL ADDRESSING

IP Addresses: Classful Addressing

CONTENTS • INTRODUCTION • CLASSFUL ADDRESSING • Different Network Classes • Subnetting • Classless Addressing • Supernetting • CIDR (classless Interdomain Routing)

4. 1 INTRODUCTION

What is an IP Address? An IP address is a 32 -bit address. The IP addresses are unique.

Address Space …………. . addr 15 addr 2 …………. . addr 41 addr 226 addr 31 …………. .

Address space rule …………. . addr 15 …………. . Theaddr 2 address space in a protocol …………. . That uses N-bits to define an addr 41 addr 226 Address is: addr 31 N …………. . 2 …………. .

IPv 4 address space The address space of IPv 4 is 232 or 4, 294, 967, 296.

Binary Notation 01110101 10010101 00011101010

Figure 4 -1 Dotted-decimal notation

Hexadecimal Notation 0111 0101 1001 0101 0001 1110 1010 75 95 1 D 0 x 75951 DEA EA

Example 1 Change the following IP address from binary notation to dotted-decimal notation. 10000001011 11101111 Solution 129. 11. 239

Example 2 Change the following IP address from dotted-decimal notation to binary notation: 111. 56. 45. 78 Solution 01101111 00111000 00101101 01001110

Example 3 Find the error in the following IP Address 111. 56. 045. 78 Solution There are no leading zeroes in Dotted-decimal notation (045)

Example 3 (continued) Find the error in the following IP Address 75. 45. 301. 14 Solution In decimal notation each number <= 255 301 is out of the range

Example 4 Change the following binary IP address Hexadecimal notation 10000001011 11101111 Solution 0 X 810 B 0 BEF or 810 B 0 BEF 16

CLASSFUL ADDRESSING

Figure 4 -2 Occupation of the address space

In classful addressing the address space is divided into 5 classes: A, B, C, D, and E.

Figure 4 -3 Finding the class in binary notation

Figure 4 -4 Finding the address class

Example 5 Show that Class A has 231 = 2, 147, 483, 648 addresses

Example 6 Find the class of the following IP addresses 00000001011 11101111 11000001011 11101111 Solution • 00000001011 11101111 1 st is 0, hence it is Class A • 11000001011 11101111 1 st and 2 nd bits are 1, and 3 rd bit is 0 hence, Class C

Figure 4 -5 Finding the class in decimal notation

Example 7 Find the class of the following addresses 158. 223. 1. 108 227. 13. 14. 88 Solution • 158. 223. 1. 108 1 st byte = 158 (128<158<191) class B • 227. 13. 14. 88 1 st byte = 227 (224<227<239) class D

IP address with appending port number • 158. 128. 1. 108: 25 • the for octet before colon is the IP address • The number of colon (25) is the port number

Figure 4 -6 Netid and hostid

Figure 4 -7 Blocks in class A

Millions of class A addresses are wasted.

Figure 4 -8 Blocks in class B

Many class B addresses are wasted.

Figure 4 -9 Blocks in class C

The number of addresses in a class C block is smaller than the needs of most organizations.

Class D addresses are used for multicasting; there is only one block in this class.

Class E addresses are reserved for special purposes; most of the block is wasted.

Network Addresses The network address is the first address. The network address defines the network to the rest of the Internet. Given the network address, we can find the class of the address, the block, and the range of the addresses in the block

In classful addressing, the network address (the first address in the block) is the one that is assigned to the organization.

Example 8 Given the network address 132. 21. 0. 0, find the class, the block, and the range of the addresses Solution The 1 st byte is between 128 and 191. Hence, Class B The block has a netid of 132. 21. The addresses range from 132. 21. 0. 0 to 132. 21. 255.

Default Mak • Class A default mask is 255. 0. 0. 0 • Class B default mask is 255. 0. 0 • Class C Default mask 255. 0